SPX Bollinger Band Historical Extreme

The recent drop from the SPX has proven abrupt, but it may be historically so. Using a weekly chart and Bollinger Bands - standard 20-period MA and 2 standard deviation settings - we find price marked its biggest downside move beyond the lower bounds of 2 standard deviations on records I have going back 30 years. I don't consider this a buy signal though given the extreme one-sided activity of the past six years.